U.S. patent application number 13/120859 was filed with the patent office on 2011-12-08 for electric motor/gear mechanism unit.
This patent application is currently assigned to MAXON MOTOR AG. Invention is credited to Franzxaver Folmli, Hugo Fritschy, Raniero Pittini, Jens Oliver Schulze, Daniel Sherwin, Dirk Zimmermann.
Application Number | 20110298322 13/120859 |
Document ID | / |
Family ID | 41055143 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110298322 |
Kind Code |
A1 |
Sherwin; Daniel ; et
al. |
December 8, 2011 |
ELECTRIC MOTOR/GEAR MECHANISM UNIT
Abstract
The invention relates to an electric motor/gear mechanism unit
including a housing, an iron-free rotor winding rotatably arranged
in the interior of the housing, a collector connected to the rotor
winding, a rotor shaft extending through the collector, and a gear
mechanism which is connected to the rotor shaft and which has an
output shaft. The present invention is so conceived that the gear
mechanism is produced from a non-magnetic material and arranged in
the interior of the rotor winding.
Inventors: |
Sherwin; Daniel; (Jerusalem,
IL) ; Fritschy; Hugo; (Sachseln, CH) ; Folmli;
Franzxaver; (Oberdorf, CH) ; Schulze; Jens
Oliver; (Giswil, CH) ; Pittini; Raniero;
(Hergiswil, CH) ; Zimmermann; Dirk; (Sexau,
DE) |
Assignee: |
MAXON MOTOR AG
Sachseln
CH
|
Family ID: |
41055143 |
Appl. No.: |
13/120859 |
Filed: |
November 30, 2009 |
PCT Filed: |
November 30, 2009 |
PCT NO: |
PCT/EP2009/008518 |
371 Date: |
August 22, 2011 |
Current U.S.
Class: |
310/83 |
Current CPC
Class: |
H02K 23/58 20130101;
H02K 9/00 20130101; H02K 3/47 20130101; H02K 1/2706 20130101; H02K
7/116 20130101; H02K 1/223 20130101 |
Class at
Publication: |
310/83 |
International
Class: |
H02K 7/116 20060101
H02K007/116 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2008 |
IL |
195613 |
Claims
1. An electric motor/gear mechanism unit (20) comprising a housing
(1), an iron-free rotor winding (2) rotatably arranged in the
interior of the housing (1), a collector (4) connected to the rotor
winding (2), a rotor shaft (10) extending through the collector
(4), and a gear mechanism (9) which is connected to the rotor shaft
(10) and which has an output shaft (7), characterized in that the
gear mechanism (9) is arranged in the interior of the rotor winding
(2), that it consists of an internally toothed annulus gear (28),
and that the gears (9A, 9B, 9C, 9D) meshing therewith are produced
from a non-magnetic material.
2. An electric motor/gear mechanism unit (20) according to claim 1,
characterized in that a hollow permanent magnet (3) is arranged in
the interior of the rotor winding (2).
3. An electric motor/gear mechanism unit (20) according to one of
the claim 1 or 2, characterized in that the housing (1) and the
annulus gear (28) consist of a magnetically soft material.
4. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 3, characterized in that the rotor shaft (10) and
the output shaft (7) are in alignment with one another.
5. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 4, characterized in that the gear mechanism (9) is
a planetary gear unit.
6. An electric motor/gear mechanism unit (20) according to claim 5,
characterized in that the planetary gear unit (9) is configured
such that it comprises at least one stage, each gear stage
comprising a planetary carrier (31, 32, 33, 14) which is rotatable
about an axis of rotation (29), a sun gear, an annulus gear (28)
and at least one planet gear (9A, 9B, 9C, 9D), the end face of the
planetary carrier (31, 32, 33, 14) further being provided with at
least one journal (27) which projects therefrom and on which the
planet gear (9A, 9B, 9C, 9D) is rotatably supported, and at least
said at least one planet gear (9A) of the first gear stage being
implemented such that it is at least radially displaceable relative
to the axis of rotation (29) of the planetary carrier (31).
7. An electric motor/gear mechanism unit (20) according to claim 6,
characterized in that at least said at least one journal (27) of
the planetary carrier (31) of the first gear stage has a
substantially elliptical cross-section.
8. An electric motor/gear mechanism unit (20) according to one of
the claims 5 to 7, characterized in that the rotor shaft (10) has,
on its end facing the gear mechanism, external teeth defining the
sun gear (13) of the first gear stage, the outer diameter of said
external teeth of the rotor shaft (10) corresponding to the
diameter of the rotor shaft (10).
9. An electric motor/gear mechanism unit (20) according to one of
the claims 5 to 8, characterized in that at least the teeth of the
gears of the first gear stage are hardened or provided with a hard
layer.
10. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 9, characterized in that the housing (1) is
provided with cooling fins and/or with internal and/or external
cooling channels.
11. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 10, characterized in that the gear mechanism (9)
can be replaced and/or relubricated.
12. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 11, characterized in that the gear mechanism (9) is
filled with oil.
13. An electric motor/gear mechanism unit (20) according to one of
the claims 2 to 12, characterized in that the hollow permanent
magnet (3) is composed of magnet segments.
14. An electric motor/gear mechanism unit (20) according to one of
the claims 1 to 13, characterized in that the rotor shaft (10) is
supported such that it is axially preloaded by means of a spring or
a spring plate.
Description
[0001] The invention relates to an electric motor/gear mechanism
unit according to the preamble of claim 1.
[0002] Electric motor/gear mechanism units according to the prior
art are known e.g. from U.S. Pat. No. 4,918,344, U.S. Pat. No.
5,662,545, U.S. Pat. No. 6,500,087, U.S. Pat. No. 7,211,016,
US2004/0095037 and GB1007524A. The electric motor/gear mechanism
units described there have a common housing for the electric motor
and the gear mechanism. In many fields of use, there is an
increasing demand for extremely compact electric motor/gear
mechanism units, in particular for those having a high torque.
There is an ever increasing demand for a compact structural design
of the axial as well as of the radial dimensions of electric
motor/gear mechanism units. The electric motor/gear mechanism units
known from the prior art can no longer satisfy future demands and
some of them require a high production outlay.
[0003] It is therefore the object of the present invention to
provide an extremely compact electric motor/gear mechanism unit
having a high torque. This object is achieved by the features of
claim 1. The invention starts from an electric motor/gear mechanism
unit comprising a housing, an iron-free rotor winding rotatably
arranged in the interior of the housing, a collector connected to
the rotor winding, a rotor shaft extending through the collector,
and a gear mechanism which is connected to the rotor shaft and
which has an output shaft. A solution according to the present
invention is provided when the gear mechanism is arranged in the
interior of the rotor winding, and when it consists externally of
an annulus gear, which is preferably produced from a magnetic
material, whereas the movable parts of the gear mechanism are
produced from a non-magnetic material. Electric motors with an
iron-free rotor winding normally have a very compact structural
design in the radial direction. Making use of the solution
according to the present invention a very compact structural design
of the whole electric motor/gear mechanism unit is achieved also in
the axial direction. Due to the fact that the annulus gear is
produced from magnetic material, it also serves as a magnetic yoke
for the magnetic circuit of the motor. The magnetic field of the
permanent magnet will hardly enter the interior of the gear
mechanism, when the gears meshing with the annulus gear are
produced from a non-magnetic material. Losses caused by a reversal
of magnetism, eddy currents and magnetic pressure forces are
avoided in this way. In addition, the dual function of the gear
mechanism housing can be used insofar as there will be more room
for the gear mechanism, which means that the gear mechanism can be
provided with a more stable structural design.
[0004] Advantageous further developments of the present invention
are the subject matter of the subclaims.
[0005] According to a preferred embodiment of the present
invention, a hollow permanent magnet is arranged in the interior of
the rotor winding. This hollow permanent magnet is connected to the
housing of the electric motor and defines thus the stator of the
electric motor. The hollow permanent magnet encloses the gear
mechanism of the electric motor/gear mechanism unit. On the basis
of this structural design, very high degrees of efficiency of the
electric motor and, consequently, of the entire electric motor/gear
mechanism unit can be achieved.
[0006] Alternatively, the hollow permanent magnet may also be
arranged outside of the rotor winding so that it encloses the rotor
winding. In this case, the hollow permanent magnet can define the
housing of the electric motor/gear mechanism unit. If an additional
housing should be provided, it can be produced from a magnetic
material and thus define a magnetic yoke.
[0007] According to another preferred embodiment of the present
invention, the rotor shaft and the output shaft are in alignment
with one another.
[0008] In accordance with another preferred embodiment, the gear
mechanism is a planetary gear unit. Planetary gear units allow a
realization of extremely high reduction ratios in combination with
a compact structural design. Alternatively, spur gear units or
bevel gear units may be used as well.
[0009] According to another preferred embodiment of the present
invention, the planetary gear unit is configured such that it
comprises at least one stage. The first gear stage of a planetary
gear unit, which is connected to the rotor shaft, normally has
applied thereto the highest loads. Each gear stage of planetary
gear unit comprises a planetary carrier which is rotatable about an
axis of rotation, a sun gear, an annulus gear and at least one
planet gear. The end face of the planetary carrier is provided with
a journal for each planet gear, said journal projecting from said
end face and the planet gear being rotatably supported thereon by
means of an axial bore. In view of manufacturing tolerances, high
friction losses may occur between planet gears and the sun gear and
annulus gear, respectively. This leads to a generation of a large
amount of heat and to a short service life of the planetary gear
unit. The friction losses can be reduced, when there is a certain
amount of play between the planet gears and the sun gear and
annulus gear, respectively. This is preferably achieved in that the
planet gears are radially displaceable with respect to the axis of
rotation of the planetary carrier. To this end, the journals of the
planetary carrier are preferably implemented such that they have a
substantially elliptical cross-section. The shorter one of the two
principal axes of the ellipse extends in the radial direction of
the planetary carrier. The measures for providing a certain amount
of play between the planet gears and the sun gear and annulus gear,
respectively, are preferably taken for the first stage of the
planetary gear unit. They may, however, also be taken for the other
stages of the planetary gear unit, if the planetary gear unit
should comprise more than one gear stage. The play provided reduces
the friction losses. This will also lead to a reduction of heat
development and to a longer service life of the gear mechanism.
[0010] According to another preferred embodiment of the present
invention, the rotor shaft has, on its end facing the gear
mechanism, external teeth defining the sun gear of the first gear
stage of a planetary gear unit. The outer diameter of said external
teeth of the rotor shaft corresponds to the diameter of the rotor
shaft itself. In the case of this embodiment, a pinion, which
normally defines the sun gear of the first gear stage, need not be
attached to the rotor shaft. The diameter of the sun gear is
therefore smaller than in the case of an attached pinion. It is
thus possible to accomplish a higher reduction ratio, whereby the
torque of the electric motor/gear mechanism unit is increased.
[0011] According to a preferred embodiment, at least the teeth of
the gears of the first gear stage are hardened or provided with a
hard layer. In the case of non-magnetic metallic materials, said
hardening can be carried out by means of a surface treatment, such
as a chemical or a thermal treatment. This will increase the
service life of the gear mechanism. In view of the high production
costs for hardening or coating processes, the latter are only
carried out in the first, highly loaded gear stage of the planetary
gear unit. A suitable base material is e.g. non-magnetic steel.
Alternative materials for the gears of the gear mechanism are
particularly hard plastic materials, metallic glass or ceramic
materials.
[0012] The service life of the electric motor/gear mechanism unit
can be increased still further, when the housing is provided with
cooling fins and/or with internal and/or external cooling channels
for improved heat dissipation. The heat of the gear mechanism, the
permanent magnet and the rotor winding is transferred to the
housing via the air gap between the rotor and the stator. An
improved dissipation of heat is accomplished, when the bearing seat
of the rotor or of the rotor shaft has a large contact area.
[0013] In view of the fact that the service life of the electric
motor exceeds that of the gear mechanism many times, even if more
intensive measures are taken for increasing the service life of the
gear mechanism, the gear mechanism is preferably adapted to be
replaced and/or relubricated.
[0014] According to another preferred embodiment of the present
invention, the gear mechanism is filled with oil so as to increase
its service life.
[0015] Hollow-cylindrical permanent magnets are comparatively
expensive to produce. According to another preferred embodiment of
the present invention, the hollow stator permanent magnet is
therefore composed of magnet segments. This allows production at a
reasonable price.
[0016] In order to accomplish a better guidance of the rotor or the
rotor winding and in order to avoid the rotor winding from rubbing
against components of the stator, the rotor shaft is supported such
that it is axially preloaded by means of a spring or a spring
plate. To this end, a preloaded bearing seat is preferably provided
in the brush cover.
[0017] In the case of the electric motor/gear mechanism unit
according to the present invention, various electric motors can be
used. It is imaginable to use e.g. alternating current as well as
direct current motors, mechanically commutated or brushless motors
and stepping motors.
[0018] In the following, a preferred embodiment of the present
invention will be explained in more detail making reference to the
drawings, in which:
[0019] FIG. 1 shows an oblique view, part of which is a sectional
view, of an electric motor/gear mechanism unit according to the
present invention.
[0020] FIG. 2 shows a straight longitudinal sectional view of the
electric motor/gear mechanism unit according to the present
invention shown in FIG. 1.
[0021] FIG. 3 shows the planetary carrier of the first stage of the
planetary gear unit of the electric motor/gear mechanism unit
according to the present invention as shown in FIGS. 1 and 2.
[0022] FIGS. 1 and 2 show an electric motor/gear mechanism unit 20
according to a preferred embodiment of the present invention. The
electric motor/gear mechanism unit 20 essentially comprises a
bell-type armature motor with an iron-free rotor winding 2 of a
known structural design, and a planetary gear unit 9 installed in
the interior of the hollow cylindrical bell-type armature motor.
The housing 1 of the electric motor/gear mechanism unit 20
according to the present invention has a brush cover-side end 15
and an output-side end 16. At the output-side end 16 the housing 1
merges with a neck portion 18 via an area of reduced width 17. In
the interior of the housing 1 and concentrically therewith, an
iron-free rotor winding 2 is arranged. This iron-free rotor winding
2 is connected via the collector 4 to the rotor shaft 10, coaxially
with said rotor shaft and such that it is secured against rotation
relative thereto. At the brush cover-side end 15 of the housing 1,
the housing 1 is closed by a brush cover 12. The whole rotor
including the iron-free rotor winding 2 is rotatably supported in
the brush cover via the bearing 6 such that it is concentric with
the housing 1. In the direction of the output-side end 16 of the
housing, the rotor shaft 10 is, in addition, rotatably supported,
via the bearing 5, on the hollow permanent magnet 3, which is
connected to the housing 1 such that it is secured against rotation
relative thereto. The rotor shaft 10 is supported in the bearing 5
via a small step-shaped flange 23 of the rotor shaft 10. The hollow
cylindrical permanent magnet 3 extends around an annular support
wall 26 after the fashion of a sleeve and is enclosed by an
iron-free rotor winding 2. Between said iron-free rotor winding 2
and the hollow cylindrical permanent magnet 3 a small air gap is
formed. In FIG. 1 it can be seen that the bell-type armature motor
is configured as a brush-commutated motor. The commutation is
effected via two carbon brushes 11 which slide over the collector 4
and which are held by the brush holders 21 and 22. The electric
connection of the two carbon brushes 11 is established via the two
connection cables 24.
[0023] On the rotor shaft end facing the interior of the electric
motor/gear mechanism unit a pinion 13 defines the sun gear of the
first gear stage of a four-stage planetary gear unit 9. The annulus
gear 28 which the four gear stages have in common also defines the
housing of the planetary gear unit 9. It follows that the planetary
gear unit 9 defines an independent unit and can be installed in the
interior of the bell-type armature motor in a fully mounted
condition. The annulus gear 28 of the planetary gear unit 9 abuts
on the annular support wall 26 of the housing 1 of the electric
motor/gear mechanism unit 20 such that it is concentric and flush
with said support wall 26. In FIG. 2, the planet gears of the gear
stage are designated by reference numeral 9A, the planet gears of
the second gear stage by reference numeral 9B, those of the third
stage are, in a corresponding manner, designated by 9C, and those
of the fourth stage by 9D. Furthermore, the planetary carriers of
the first, second, third and fourth stages are sequentially
designated by reference numerals 31, 32, 33 and 14. The planetary
carriers of the first, second and third stages are connected to the
sun gear of the respective subsequent stage. The planetary carrier
14 of the fourth stage simultaneously defines the flange for the
output shaft 7 whose axis coincides with the axis of the rotor
shaft 10. The output shaft 7 is rotatably supported via two
bearings 8 in the neck portion 18 of the housing 1 of the electric
motor/gear mechanism unit 20. All the sun gears, planet gears,
planetary carriers as well as the annulus gear 28 of the planetary
gear unit 9 are produced from non-magnetic materials so as to avoid
interference and/or losses during operation of the electric
motor/gear mechanism unit. In addition, the highly loaded first
stage of the planetary gear unit 9 is provided with toothings
hardened by surface finishing. Also the other components of the
planetary gear unit 9, in particular the components of the other
stages of he planetary gear unit, may at least be surface hardened
or produced from particularly wear resistant non-magnetic
materials. Reference should be made to the fact that, depending on
the desired reduction ratio or depending on the desired torque of
the output shaft 7, also planetary gear units comprising one to
three stages may be used. Theoretically, it would also be possible
to use a planetary gear unit comprising five or more stages, but
the friction losses in the case of planetary gear units comprising
five or more stages are so high that such planetary gear units are
normally not used.
[0024] In FIG. 3 the planetary carrier 31 of the first gear stage
of the planetary gear unit 9 is shown. In order to reduce the
friction and the heat development in the first stage, the planet
gears 9A of the first gear stage are intentionally supported with a
certain amount of play. This intentional play is a play in the
radial direction with respect to the axis of rotation 29 of the
planetary carrier 31, which, due to the coaxial arrangement of the
motor and the gear mechanism and due to the engagement of the
pinion 13, coincides with the axis of rotation of the rotor shaft
10. Each of the planet gears 9A of the first gear stage is
rotatably supported on a respective journal 27 of the planetary
carrier 31 by means of a hollow cylindrical bore, said journals 27
being shown in FIG. 3. The journals 27 extend perpendicularly from
the end face of the planetary carrier 31 parallel to the rotor
shaft 10 and to the whole longitudinal axis of the electric
motor/gear mechanism unit 20. The cross-section of the journals 27
is elliptical so that the shorter principal axis of the elliptical
cross-section extends radially with respect to the axis of rotation
29 of the planetary carrier 31. The longer principal axis of the
ellipse corresponds approximately to the diameter of the axial bore
of the planet gears 9A. It follows that the planet gears 9A are
supported with play in the radial direction with respect to the
axis of rotation 29 of the planetary carrier 31. Due to the fact
that they are supported with play, their optimum position with
respect to the sun gear 13 of the first stage and the annulus gear
28 will be obtained automatically on the basis of the tolerances.
Whereas in the case shown, three planet gears and three journals
are provided, it is also possible to provide a different number of
planet gears per stage. The embodiment that has been chosen in FIG.
3 for the planetary carrier 31 of the first gear stage of the
planetary gear unit 9 can also be chosen for the other stages.
[0025] When the service life of the old planetary gear unit 9 has
come to an end, said old planetary gear unit 9 can be removed from
the electric motor/gear mechanism unit as a separate subunit so
that a new planetary gear unit 9 can be installed into the electric
motor/gear mechanism unit 20. In addition to the already discussed
measures taken for increasing the service life of the planetary
gear unit 9, the planetary gear unit may also be completely filled
with oil so as to accomplish an improved heat transfer. The oil
also serves the purpose of lubrication. Cooling and heat
dissipation of the electric motor/gear mechanism unit 20 is
effected via cooling fins of the housing 1, which are not shown.
Cooling can be improved still further through cooling channels in
the housing 1.
* * * * *